Known in the art is an adhesive composition containing at least 50% by weight of a monomeric ester of .alpha.-cyanacrylic acid, a modifying agent consisting of 1 to 49% by weight of a monomeric monofunctional (with one double bond) alkylacrylate and 1 to 15% by weight of a bifunctional (with two double bonds) monomer such as an alkylacrylate or divinylbenzene (cf. U.S. Pat. No. 2,816,093).
This prior art adhesive composition has a disadvantage residing in that an initiator should be added thereinto for curing which does not provide for a possibility of storing said composition, since it is unstable in the presence of an initiator. Furthermore, the use of said adhesive composition with the necessity of adding an initiator complicates the technology of bonding.
Also known in the art is an adhesive composition consisting of 20 to 95% by weight of a monomeric ester of .alpha.-cyanacrylic acid, 80 to 5% by weight of a modifying agent, viz, a monomeric methylenemalononitrile (cf. U.S. Pat. No. 2,763,585).
This prior art composition has a disadvantage residing in that it is readily hydrolyzable and, consequently, nonwater-resistant.
Another disadvantage of this prior art adhesive composition is that the second monomer, i.e., methylenemalononitrile, though enhancing adhesive properties of the monomeric ester of .alpha.-cyanacrylic acid (since it may be used per se as an adhesive), it forms, however, a rigid film and the ester of .alpha.-cyanacrylic acid should act as a plastifying agent therefor. Consequently, to obtain a flexible adhesive film, it is necessary to use a monomeric ester of .alpha.-cyanacrylic acid with a long-chain radical which is economically inefficient.
Still another disadvantage of this prior art adhesive composition resides in that the commercial-scale synthesis of methylenemalononitrile is very complicated.
Further known in the art is an adhesive composition consisting of 70 to 95% by weight of a monomeric ester of .alpha.-cyanacrylic acid and 30 to 5% by weight of a modifying agent, i.e., dimethylvinylethynylcarbinol or monomeric derivatives thereof of the formula: ##STR2## wherein R is H, CH.sub.3, C.sub.2 H.sub.5, C.sub.4 H.sub.9, CH.sub.2 CH.sub.2 CN, COCH.sub.3 and the like (cf. USSR Inventor's Certificate No. 280732).
Said adhesive composition has a high mechanical strength (150 kgf/cm.sup.2) and elasticity of the adhesive joint.
However, this adhesive composition also has an essential disadvantage which resides in its low water-resistance which restricts the field of its application.